> Dick: Tell me more about this problem I may have missed something. Have
> experienced no difficulties in the last 5 -7 years during those January
days
> when its -40 to -45 F. 73 de VE3AD
The symptom is that the Tailtwister won't start on the first attempt on a
cold day. On the manual controller, you release the brake, hit the
directional control, and nothing happens. Rocking the rotor back and forth
by alternating directions eventually gets the rotor going. Hy-Gain is well
aware of the problem: they programmed the DCU-1 digital controller to
briefly move in the opposite direction when the Start button is pushed --
this simulates rocking, which can't otherwise be done due to time delays
built into the controller. So, if you repeatedly hit Start, the rotor will
begin to move. In my case, the number of times you have to do this depends
on the temperature. It starts happening whenever the temp drops below 32
degrees and the rotor has been idle for at least a few hours. Usually it
takes only one or two attempts to get it going. As the temperature drops, it
takes more and more attempts. On a really cold day, maybe 10-20 below zero,
it can take six attempts. Also, the amount of time the rotor has to sit idle
for the problem to occur decreases as the temp drops. It can get as low as
an hour or less. Makes those winter contests tough!
I have a U.S. Tower 72' tubular with a TH-7 on top. Two of our local club
members used Tailtwisters on their 100' Rohn 45 towers with a TH-7 and
shorty forty at the top. Both had exactly the same problem. One guy
eventually dumped the Tailtwister for the big Yaesu rotor and hasn't had a
problem since. The other guy has the problem even in the summer now. His
problem seems to be related to how long the rotor sits idle. What we had in
common is that we all live within a few miles of each other in Western NH,
had Tailtwister and TH-7s.
About 18 months ago I queried the reflector about the problem. The response
was overwhelming -- a lot of people were having the problem. One guy told me
he did a survey that showed something like 80 out of 90 respondants were
having the problem with their Tailtwisters. My impression was that those in
northern climates had more problems.
There has been a lot of speculation about the cause. Some will tell you it's
the grease. Others will tell you its the wedge. Yet others will tell you
it's rusty ball bearings. A few years back, Hy-Gain changed to a low-temp
grease, but my Tailtwister was made after that.
I contacted Hy-Gain about the problem, and found that they knew all about it
but had not been able to detemine the cause. I volunteered to help them
track down the problem -- I have the dual advantages of living in a very
cold winter climate and having a rotor that is bottom mounted (it turns the
whole tower.) It's relatively easy to remove and replace a rotor in my
tower, even when it's 15 degrees outside (not something I'd want to do all
the time, but a heck of a lot better than trying to do it at the top of a
100' tower!)
We missed the first winter, but this year we managed to run one test. A
technician at the factory had noticed that the spline spacing on the
Tailtwister rotor housing was much narrower than on their other rotors, and
that the matching brake wedge splines fit in there pretty tightly. He
figured that this might make it harder to pull the wedge back. He then
discovered that an oval opening in the brake wedge could actually allow the
solenoid shaft to pull back without bringing the wedge with it. He
speculated that if the brake wedge splines were being held tightly by the
splines on the housing, there might be enough friction for the shaft to
slip. The result would be that you would hear the "clang" of the shaft
retracting, but the wedge would remain engaged in the housing. The
technician also speculated that wind load on the antenna mast might cause
the wedge splines to get more tightly meshed with the splines on the
housing.
The technician worked with the engineers to redesign the opening in the
brake wedge so that the shaft couldn't slip. They sent me a brand new
(unmodified) rotor, and had me return my old one. I installed the
replacement rotor and used it while they modified the brake wedge in my old
rotor. They sent my rotor back and I installed it. It worked fine for a few
days, then began to fail in exactly the same manner as before. Within a
month, it was as bad as it had been before the modification. End of test.
The good news for me was that the replacement rotor worked fine, even in
very cold temperatures. Hy-Gain let me send back the old rotor and keep the
new one (they should have -- I reported the problem when it was still under
warranty.) If it ever fails again, I'm going to replace it with another
brand.
By the way, the Hy-Gain technician seemed to resist the notion that my
problem had something to do with temperature. But after I repeated the exact
correlation between the problem and the temperature several times, he
started to listen. I suggested that the problem seemed to be related to the
freezing temperature of water. I speculated that water vapor could be
entering the housing (it's not sealed) and freezing on some interface. The
rocking breaks or melts the ice, freeing the rotor. Then, after the rotor
has sat idle for a while, the water freezes again. The colder it is, the
faster the water freezes. The technician said there were two cork disks
inside the motor that act as a brake when the motor stops, and that possibly
they were absorbing water and freezing. That was the last I heard about it.
So, the problem seems to afflict only certain Tailtwisters, and only under
certain loading conditions. Sometimes temperature is a major factor,
sometimes it's not. My guess is that there is more than one design problem,
so symptoms and solutions might vary.
Perhaps this information will be of use to someone.
73, Dick, WC1M
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